# How to dim led circuit?

#### NVZN1

Joined Dec 17, 2016
34
Hello, I have a desk light that can be dimmable by touch sensors. Unfortunately it failed, and I managed to know their working voltages.

Very dim light : 2.3V
Maximum brightness : 2.7V

Now I wanted to bypass the original circuit since it failed, can I do this with a potentiometer as dimmer and on off switch?

If yes, I need the diagram illustration.. Because I'm quite newbie in this sector... And also how many K ohm potentiometer needed?

Thank you!

#### DickCappels

Joined Aug 21, 2008
9,632
Do you mind building a simple electronic circuit using an inexpensive 8 pin integrated circuit?

You need to choose resistors that limit the LED current to whatever your LEDs can handle. If describewhat is conneceted to the LED, particularly resistors, we might be able to get you close to the right value.

Here is a Google search that found this and many similar circuits:

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#### NVZN1

Joined Dec 17, 2016
34
Do you mind building a simple electronic circuit using an inexpensive 8 pin integrated circuit?
View attachment 276665
You need to choose resistors that limit the LED current to whatever your LEDs can handle. If describewhat is conneceted to the LED, particularly resistors, we might be able to get you close to the right value.

Here is a Google search that found this and many similar circuits:
Does 555 support 4.2v input?

#### Alec_t

Joined Sep 17, 2013
13,337
Yes, if it's a CMOS version.

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#### Jerry-Hat-Trick

Joined Aug 31, 2022
232

This assumes that it's a single LED and the maximum current is 20mA. I'm thinking, typically a white LED has a voltage drop higher than 2.3 to 2.7 Volt so I do wonder if something else is going on? Not as elegant as a 555 with variable mark/space but quick to make!

#### Audioguru again

Joined Oct 21, 2019
5,599
Your 18650 Lithium-Ion battery cell is not always 4.2V. Its voltage drops to 3.0V as it is used,
The LM555 and NE555 both have a spec'd minimum supply voltage of 4.5V so they will not work with your battery cell.

My solar garden lights lightup a 3.2V white, blue or colors-changing LED when the battery voltage drops to 0.9V with a voltage stepup circuit.

#### bassbindevil

Joined Jan 23, 2014
687
This PWM dimmer/speed control claims to work down to 3V. Maybe they have a newfangled version of the 555? TI's LMC555 can work down to 1.5V.
https://www.ebay.com/itm/172973475852
You may need to bridge a jumper for low-voltage operation (or remove a voltage regulator, or series diode).

#### Audioguru again

Joined Oct 21, 2019
5,599
Enhancing the photo of the 555 IC shows that it is a Cmos TLC555.

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